The invention relates to the field of solar energy collection and comprises an improved heliostat construction utilizing rigid mirrors as compressive struts in a flexible tensioned wire framework.
In recent years solar energy has been recognized as a prime and virtually infinite source of inexpensive energy but improved collection systems are urgently needed in order to gather the sun's energy at a cost reasonably competitive with other fuels. For large scale collection of solar energy, arrays of heliostats have been found desirable.
Heliostats utilize a sun reflecting mirror which is carried by a mechanical framework and generally include control systems to track the sun and cause the solar energy to be reflected to a target where the light energy is utilized or converted to other forms of energy. Present heliostats utilize pedestal mountings which are expensive and require heavy steel or concrete frameworks for support of the mirror. Typically, the larger the mirror surface, the greater the amount of steel and concrete needed to effectively anchor and stabilize the structure against the wind forces to which larger mirrors are subjected. Recent studies have determined that for each square foot of mirror surface used in a heliostat, approximately eight pounds of steel framework are needed for its support. A large heliostat utilizing a 300 square foot mirror can require a ten ton foundation. With these problems in mind, it is crucial to develop heliostats which do not require such expensive and massive support systems.
In order for solar energy to become a practical source of new energy, it is desirable to develop an inexpensive heliostat which is practical, long lasting and easy to build and maintain. Efforts have been directed to reducing the weight of the heliostat, as in U.S. Pat. Nos. 3,843,238, 4,251,135 and 4,134,387 by eliminating the traditional rigid mirror and replacing it with a thin, reflective synthetic film which is stretched by a lightweight frame. While such a mirror structure reduces heliostat weight and permits lighter structural support components, it is more vulnerable to weather damage and deterioration, and its tendency toward optical distortion and deformation by wind loads has questioned its long term utility.
To meet long term United States energy requirements for electrical power, studies have suggested solar energy farms occupying the deserts of the western United States. Current United States heat energy requirements for electrical energy generation are on the order of 78 quadrillion BTU. Since under ideal conditions approximately 300 BTU per square foot per hour can be obtained from sunlight, assuming a conversion rate of 10 to 20 percent efficiency, then tens of thousands of square miles of heliostat structures would be required to meet United States requirements.
If energy independence is to be realized by utilization of solar energy, the challenge of building such a massive system of heliostats at a rate of construction which exceeds the rate of deterioration will require a long lasting, simple, inexpensive and rapidly erected heliostat structure. The present invention is directed toward meeting this need.